Abstract

Post-transplant root growth is critical for landscape plant establishment. The Horhizotron™ provides a way to easily measure root growth in a wide range of rhizosphere conditions. Mountain laurel (Kalmia latifolia L.) plants were removed from their containers and planted in Horhizotrons in a greenhouse in Auburn, AL, and outdoors in Blacksburg, VA. Each Horhizotron contained four glass quadrants extending away from the root ball, and each quadrant within a Horhizotron was filled with a different substrate (treatment): 1) 100% pine bark (Pinus taeda L., PB), 2) 100% soil, 3) a mixture of 50:50 (by vol) PB:soil, or 4) 100% soil along the bottom of the quadrant to a depth of 10 cm (4 in) and 100% PB layered 10 cm (4 in) deep on top of the soil. Root growth along the glass panes of each quadrant was measured bi-weekly in Auburn and weekly in Blacksburg. In both locations, roots were longer in all treatments containing pine bark than in 100% soil. When pine bark was layered on top of soil, roots grew into the pine bark but did not grow into the soil. Results suggest that amending soil backfill with pine bark can increase post-transplant root growth of container-grown mountain laurel.